Injuries to knee ligaments are becoming more frequent and more extensive, demanding increased understanding of the healing process and methods to enhance it. Clinically, the injured medial collateral ligament (MCL) has been found to heal without surgical intervention; however, laboratory studies have shown that the quality of the healed tissue remains far from the normal tissue, even after one year. There are serious concerns about the suboptimal biomechanical, biochemical, and histomorphological properties of healing tissue, especially in the case of more severe injuries that involve both the MCL and anterior cruciate ligament (ACL), which may lead to the early development of osteoarthritis. There is yet no consensus of opinion on the therapeutic approach to such combined MCL/ACL injuries. New and innovative approaches, such as antisense gene therapy and functional tissue engineering, have become available. Thus, the overall objective of this study is to explore novel ways to enhance MCL healing. The proposed study involves four Specific Aims: (1) antisense oligodeoxynucleotides (ODNs) specific for collagen types V and III, alone and in combination, will be delivered to the healing MCL to reduce the ratios of collagen types V/I and III/I, thereby increasing the collagen fibril diameter; (2) a tissue-engineered small intestinal submucosa (SIS) scaffold will be applied to aid the healing MCL after rupture by improving the collagen fiber alignment; (3) the optimal treatments from above will be applied concurrently to further enhance the healing process; and (4) this treatment modality will be extended to improve MCL healing in the more severe combined MCL/ACL injury. Using an interdisciplinary approach, the biomechanical, biochemical, and histomorphological properties of the healing MCL will be evaluated. Biomechanical testing will assess joint instability, as well as the tensile and viscoelastic behaviors of the healing MCL. Biochemical analysis will include determination of collagen and proteoglycan contents, as well as typing of collagen and collagen crosslinking. Histomorphological analysis will measure the changes in collagen fibril diameter and fiber alignment. It is anticipated that increasing the diameter of collagen fibril and improving collagen fiber alignment of the healing MCL will lead to improved biomechanical properties, thereby enhancing the quality of the healing tissue. The knowledge gained from this study will enhance the understanding of the mechanisms of ligament healing, which in turn, could be applied to aid in the healing of other ligaments (ACL) and tendons (flexor tendon).